1. Field of the Invention
The present invention relates to an underwater mobile type inspection system for use in various operations, such as the ultrasonic inspection of a nuclear reactor pressure vessel in nuclear power stations, the cleaning of large containers and the recovery of foreign objects from the water.
2. Description of the Related Art
Conventionally, an ultrasonic inspection apparatus as one shown, for example, in FIG. 18 has been used as one type of inspection system for detecting defects in internal walls of large containers.
Referring to FIG. 18, an ultrasonic inspection apparatus will be described hereinbelow by way of an example which may be used to detect defects in the welded portion of the nuclear reactor pressure vessel.
In FIG. 18, the ultrasonic inspection apparatus 1 comprises a ring-like rail 4 which is attached to the outer end of the rotatable legs 6 which in turn extend radially and outwardly from the body portion thereof. The ultrasonic inspection apparatus 1 is fixed in position to an upper flange 3 of a nuclear reactor pressure vessel 2 via support legs 5 which extend from the rail 4 and a guide stud 11 when a head closure (not shown) is removed. Suspending from the body portion of the inspection apparatus 1 downwardly is a supporting column 7 along which a manipulator 10 having a probe assembly 9 may be movable by means of a driving device 8. In such a prior ultrasonic inspection apparatus 1, the positioning operation of the manipulator 10 is performed by the rotary movement of the rail 4 and the vertical movement of the driving device 8, thereby accomplishing ultrasonic inspection of any welded regions in the nuclear reactor pressure vessel 2.
FIG. 19 shows a typical example of prior art pool cleaning apparatus which is adapted to move and perform a desired operation in the water as needed.
In FIG. 19, there is shown a pool cleaning apparatus 200. The pool cleaning apparatus 200 is first transported to a pool side area, and then submerged into the pool water until it sinks to the bottom of the pool by gravity. Then, the cleaning apparatus 200 is actuated to suck and remove foreign objects or the like from the pool water by means of a pump 202, while it travels on wheels 201.
A similar cleaning operation as described above is undertaken along and on the wall surface of the pool.
FIG. 20 shows a tank cleaning apparatus which may be used to clean the inner wall surface of a container, such as a tank.
The tank cleaning apparatus 300 operates to clean the internal surface of the tank by means of a rubbing brush 302 which is attached at the top end of the apparatus body 300, while it is driven by means of screws 301 to move floating on the water surface.
Another example of an apparatus designed for flaw detection is an apparatus which is provided with a submerging device (such as one shown, for example, in the Japanese Patent Applications No.SHO 58-246435 and No.SHO 59-35508 etc.). This type of flaw detection apparatus is designed such that it comprises a submerging device body adapted to be driven to travel under the water by a propulsion unit, and the submerged device body is provided with a slewing mechanism, of two degrees of freedom as the case may be, having a probe.
However, such apparatuses as shown in FIG. 18, FIG. 19, and FIG. 20 have problems as described below.
First, the apparatus of the construction as shown in FIG. 18 needs a rail 4 which is bulky and heavy in weight for attachment on the body 2 of the large container, and other ancillary equipments, such as support legs 5, in order to guide a probe to a location where a flaw detecting operation should be undertaken. Consequently, not only does the apparatus need plenty of time and manual labors to assemble and attach and adjust these components, but also reduction of the exposure rate of operators to radiation and speed up of its operation cannot be accomplished when the apparatus is applied to detect flaws in the nuclear reactor pressure vessel. Thus, a straight forward, compact and light-weight apparatus has been desired.
Additionally, when the apparatus having the construction as shown in FIG. 19 is intended to be used in a tank provided with a nozzle or the like, the travelling range of the apparatus is restricted, and the apparatus may not perform an intended operation directed to the internal surface of the nozzle (for example, cleaning or flaw detection operation). Besides, since the means for moving the apparatus along the wall surface is the wheels 201, it is impossible for the apparatus to run over the corner portion of the tank. Thus, if the apparatus must be operated in separate and greatly spaced locations (for example, if the apparatus must be shifted in 180.degree. opposite directions along the vertical wall surface), it is necessary to lift and then shift the apparatus body 200 and guide it again to a location where an operation is to be performed, and thus plenty of time is needed.
Moreover, as to the construction as shown in FIG. 20, it is necessary to run the water out of the tank so as to lower the level, since the apparatus moves floating on the water surface, although the apparatus can quickly move in a plane. Such run of water out of the tank is time-consuming.
Additionally, when the apparatuses as shown in FIG. 19 and FIG. 20 are applied to flaw detection operation, some degree of a thrust force (normally in the magnitude of several kgf) is needed to press the probe against a subject to be proved. Furthermore, since an elevated precision in maintaining a locus of probe motion and a constant speed of traverse motion are required, the essential requirements described above may not be derived from the utilization of driving means, such as wheels 201 and propulsion screw 301, and thus the prior apparatus may not be usable in flaw detecting operation. Furthermore, since even the flaw detection device having a submerging device does not allow its submerging device body to come into contact with the internal wall surface of the large container, and the submerging device body is constantly floating in the water, its positioning control has been difficult.
As described above, there has been no apparatus provided so far which can carry out a flaw detection operation in a container with a higher work efficiency.